Injection molded caps with external undercuts are traditionally molded in cavity dies having a split mold divided into two or more arcuate segments. This usually results in mold separation or "witness" lines visibly extending longitudinally along the skirt portion of the molded cap, coincident with the mold closure lines and possibly also resulting in the presence of flash at the mold closure lines.
A cap is generally pulled from its mold by way of its core die, which militates against the presence of any peripherally extending undercuts in the skirt mold, which would otherwise cause pick-up between cap and mold interior undercut surfaces. Thus, the only usual molding provided on the external surface of the cap skirt comprises axially extending ribs, which can make a clear draw during ejection, or molded protrusions located on a small arc on the axis of withdrawal motion of a mold segment.
From the foregoing it has followed that decoration of the outside surface of a mold skirt, with an absence of mold seams and associated witness lines cannot be satisfactorily accomplished.